With rapid development of radio and network communications technologies, working frequencies of communications products are increasingly high. The higher working frequencies of the communications products impose higher requirements on loss control in a transmission process. Backdrilling of a printed circuit board is a processing manner of reducing hole link loss effectively. After backdrilling is performed, a smaller length of a redundant stub (Stub) above the signal layer means smaller loss.
In the prior art, a plated through hole (Plated Through Hole, PTH) is generally backdrilled according to a pre-calculated theoretic backdrilling depth, and a conventional backdrilling test Coupon (Coupon), which is used in manufacturing a board edge of a PCB, is performed to test a backdrilling stub length, and sectioning analysis is performed to rectify a backdrilling depth. A workload of depth detection is heavy. Generally, a Coupon backdrilling depth is detected by sectioning according to a production batch, that is, a backdrilling depth is not rectified for every PCB. Due to thickness inhomogeneity of PCBs, the thicknesses of the PCBs in a same batch vary to some extent, and even thicknesses in different locations of a same PCB vary. The disadvantages of the prior art are: a deviation exists between a backdrilling depth obtained according to a test result of a conventional backdrilling Coupon location at a board edge of a PCB and a depth in an actual backdrilling location on the PCB. With a greater thickness of the PCB, an absolute value of the deviation is larger, and the deviation of the backdrilling depth is greater.
PCB functions are increasingly complex, and the extent of integration is increasingly high. Correspondingly, a PCB needs to have more layers and a larger thickness to meet PCB function design requirements, however, a backdrilling depth obtained according to the foregoing test result of a backdrilling Coupon location at a board edge of a PCB is deviated greatly, which leads to a great stub length and causes great impact on hole link loss when a high-frequency signal is transmitted.